5 - Plasma membranes

Question 1

What are the roles of membranes with a cell? (6)

Answer 1

Separates the cell’s components from its external environment.
Regulates the transport of minerals in and out via the partially permeable membrane.
Has antigens, so the organisms immune system recognizes it as not a threat.
May release chemicals that signal other cells.
Contain receptors for such chemical signals (hormones and drugs may bind to the receptors).
May be the site of chemical reactions.

Question 2

The Fluid Mosaic Model

Answer 2

Theory of cell membrane structure with proteins embedded in a sea of phospholipids

Question 3

Glycoprotein

…… attached to a …..

Answer 3

A carbohydrate chain attached to a protein molecule
Role in adhesion and as receptors for chemicals signals.
Intrinsic protein

EXAMPLES:
Receptors for the peptide hormones
Receptors for neurotransmitters

Question 4

Glycolipid

…… attached to a …..

Answer 4

A carbohydrate chain attached to a lipid

Antigens

Question 5

Cholesterol

Answer 5

A lipid with a hydrophobic and hydrophilic end.
Positioned between phospholipids and the bilayer.
Hydrophilic interaction with the head.
Hydrophobic interaction with the tail.
Cholesterol adds stability without making them to rigid
Prevents phospholipids form becoming solid and crystallizing

Question 6

Phospholipid

Answer 6

…………………………

Question 7

Intrinsic Proteins

Answer 7

Transmembrane proteins embedded through both layers of a membrane.

Question 8

Channel Proteins

Answer 8

Provide a hydrophilic channels that allows the passive movement of molecules down a concentration gradient.
held in between the hydrophobic core and the hydrophobic R-group on the outside of the protein.

Question 9

Carrier Proteins

Answer 9

Important role in active and passive transport.

This involves changing the shape of the protein

Question 10

How does the temperature affect the membrane?

Answer 10

When temperature increases the kinetic energy increases so the phospholipids move more.
This makes the membrane more fluid and it begins to lose its structure

Question 11

How do solvents affect the membrane?

Answer 11

Water is essential in the in the formation of phospholipid bilayer. The charged phosphate heads interact with the water keeping the bilayer intact.

Organic solvents will dissolve in membranes disrupting the cells. So alcohol is used in antiseptics to dissolve membranes of bacteria killing them.

Question 12

Diffusion

Answer 12

Movement of molecules from an area of high concentration to a low concentration across a high concentration.

Question 13

Facilitated diffusion

Answer 13

Movement of molecules from an area of high concentration to a low concentration across a high concentration across a partially permeable membrane via protein channels or carriers.

Question 14

Why is diffusion a passive process?

Answer 14

They are described as passive processes as thy only use the kinetic energy of the cell and do NOT us ATP.

Question 15

Factors affecting diffusion (3)

Answer 15

Temperature: as temp increase the KE increases, faster diffusion
Diffusion Distance: Thicker membrane, slower diffusion
Size of molecule: Smaller molecule, faster diffusion

Question 16

Osmosis

Answer 16

A region where there is more water molecules to an area where there are fewer water molecules across a partially permeable membrane.

Question 17

Water Potential

Answer 17

Pure water has the highest water potential of 0.

Solutes lower a water potential

Question 18

Animals Cells Water Potential

Answer 18

A lot of water will swell the cell and burst = Cytolysis

Lower water potential —> less water in the cell = Crenated

Question 19

Plant Cells Water Potential

Answer 19

Lots of water —> swollen cell = Turgid
Lower water potential —> less water in the cell —> cytoplasm shrinks membrane pulls away from the cell wall = Plasmolysed = Flaccid = Crenated

Question 20

Active Transport

Answer 20

The movement of substances against their concentration energy across the concentration, using ATP and protein carriers.

Question 21

Endocytosis

Answer 21

Bulk transport of molecules, too large to pass through the cell membrane, into the cell.

Question 22

Exocytosis

Answer 22

Bulk transport of molecules, too large to pass through the cell membrane, out of the cell.

Question 23

Bulk Transport

Answer 23

Some cells are too large to be transported in and out the membrane so they do this by bulk transport which requires ATP.

Question 24

Effects of solvents on phospholipids

Answer 24

Organic solvents such as acetone will damage membranes as they dissolve lipids

Question 25

Effects of the temperature on phospholipids

Answer 25

High Temperature - More KE —> permeability increases
Low Temperature - Saturated fatty acids becomes compressed - saturated fatty acids and unsaturated fatty acids maintain membrane fluidity